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At least 343 records · Page 19Linked to original sources
PubMed2002

Biological responses of Lumbriculus variegatus exposed to fluoranthene-spiked sediment.

Lumbriculus variegatus was used as a bioassay organism to examine the impact of the sediment-associated polycyclic aromatic hydrocarbon (PAH) fluoranthene on behavior, reproduction, and toxicokinetics. The number of worms increased between the beginning and end of the experiment at 59 microg x g(-1) fluoranthene, but at the next higher treatment (108 microg x g(-1)) the number of worms found was lower and not different from the control. Worms exposed to 95 microg x g(-1) also exhibited increased reproduction when fed a yeast-cerophyl-trout chow mixture. On a total biomass basis, only the 95 microg x g(-1) exposure with food exhibited a statistically significant increase over the nonfed control. Evaluation of reproduction at the two highest treatments was compromised by a brief aeration failure 2 days before the end of the experiment. The behavioral responses were followed as changes in biological burial rate (sediment reworking rate) of a 137Cs-labeled marker layer. The biological burial rate increased toward a plateau as the concentration increased from the control (3.9 microg x g(-1) dry weight total PAH) to 355 microg x g(-1) dry weight fluoranthene in sediment. The aeration failure had minimal impact on the determination of reworking rate because all the data for the rate determination were collected prior to the aeration failure. Uptake and elimination rates declined with increasing treatment concentration across the range of fluoranthene concentrations, 59-355 microg x g(-1) dry weight sediment. The disconnect between the increasing biological burial rates and the decreasing toxicokinetics rates with increasing exposure concentration demonstrates that the toxicokinetic processes are dominated by uptake and elimination to interstitial water. The bioaccumulation factor (concentration in the organisms on a wet weight basis divided by the concentration in sediment on a dry weight basis) ranged from 0.92 to 1.88 on day 10 and declined to a range of 0.52 to 0.99 on day 28 with the lowest value at the highest dose.

Animals↗
PubMed2003

Hypoxia and hypercapnia during respiration into an artificial air pocket in snow: implications for avalanche survival.

Snow avalanche case reports have documented the survival of skiers apparently without permanent hypoxic sequelae, after prolonged complete burial despite there being only a small air pocket on extrication. We investigated the underlying pathophysiological changes in a prospective, randomised 2 x 2 crossover study in 12 volunteers (28 tests) breathing into an artificial air pocket (1- or 2-l volume) in snow. Peripheral SpO(2), ETCO(2), arterialised capillary blood variables, air pocket O(2) and CO(2), snow density, and snow conditions at the inner surface of the air pocket were determined. SpO(2) decreased from a median of 99% (93-100%) to 88% (71-94%; P<0.001) within 4 min of breathing into the air pocket; the reduction was greater at 1 l, than 2 l, volume air pocket (P=0.013, intention to treat P=0.003) and correlated to snow density (r=0.50, P=0.021, partial correlation coefficient). ETCO(2) rose simultaneously from median 5.07 kPa (3.47-6.93 kPa) to 6.8 kPa (5.87-8.27 kPa; P<0.001), with consequent respiratory acidosis. Despite premature interruption due to hypoxia (SpO(2)</=75%) in 17 of 28 tests (61%), a respiratory steady state prevailed in five tests until protocol completion (30 min). We conclude that the degree of hypoxia following avalanche burial is dependent on air pocket volume, snow density and unknown individual personal characteristics, yet long-term survival is possible with only a small air pocket. Hence, the definition of an air pocket, "any space surrounding mouth and nose with the proviso of free air passages" is validated as the main criterion for triage and management of avalanche victims. Our experimental model will facilitate evaluating the interrelation between volume and inner surface area of an air pocket for survival of avalanche victims, whilst the present findings have laid the basis for future investigation of possible interactions between hypoxia, hypercapnia, and hypothermia (triple H syndrome) in snow burial.

Accidents↗
PubMedDate not supplied

The biodegradation of the fabric of soldiers' uniforms.

A study to determine the changes in the morphological structure of woollen fabric and fibres of military uniforms, after burial in biologically active soil for a particular period of time. The analysis of fabric and fibres was performed by means of organoleptic and microscopic observations. The final decay of the fabric of soldiers' uniforms took place after 5-6 weeks burial in the standardised bioactive soil. The changes of the morphological structure of fabric undergoing the process of biodegradation depended mainly on the duration of their burial in the soil.

Biodegradation, Environmental↗
PubMed1986

The method of transmission of epidemic influenza: further evidence from archival mortality data.

Evidence for influenza-associated excess mortality in the three centuries before the 20th has been sought from parish burial registers in Cumbria, Devon, Dyfed, East Anglia, Gloucestershire and Northumbria, compared with inter-epidemic years. Most of the registers showed excess of burials concordant with eight historic influenza epidemics. Comparison of the dates of these epidemics, deduced from the burials data in different areas, showed a rate of spread difficult to reconcile with direct person-to-person spread of influenza from the sick. An alternative explanation based on development of latency of the virus in the sick person and subsequent seasonal reactivation is discussed.

Disease Outbreaks↗
PubMed1992

Use of a potential of mean force to analyze free energy contributions in protein folding.

A method for calculation of the free energy of residues as a function of residue burial is proposed. The method is based on the potential of mean force, with a reaction coordinate expressed by residue burial. Residue burials are calculated from high-resolution protein structures. The largest individual contributions to the free energy of a residue are found to be due to the hydrophobic interactions of the nonpolar atoms, interactions of the main chain polar atoms, and interactions of the charged groups of residues Arg and Lys. The contribution to the free energy of folding due to the uncharged side chain polar atoms is small. The contribution to the free energy of folding due to the main chain polar atoms is favorable for partially buried residues and less favorable or unfavorable for fully buried residues. Comparison of the accessible surface areas of proteins and model spheres shows that proteins deviate considerably from a spherical shape and that the deviations increase with the size of a protein. The implications of these results for protein folding are also discussed.

Alanine↗
PubMed2000

Massive dissociation of gas hydrate during a Jurassic oceanic anoxic event

In the Jurassic period, the Early Toarcian oceanic anoxic event (about 183 million years ago) is associated with exceptionally high rates of organic-carbon burial, high palaeotemperatures and significant mass extinction. Heavy carbon-isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon, which is isotopically light. In contrast, examples of light carbon-isotope values from marine organic matter of Early Toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12C versus 13C (refs 1,2,5,6). Here, however, we report carbon-isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic, biospheric and atmospheric carbon reservoirs, and that this occurred despite the enhanced burial of organic carbon. We propose that--as has been suggested for the Late Palaeocene thermal maximum, some 55 million years ago--the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental-margin sediments.

Journal Article↗
PubMed2005

Interdomain and membrane interactions of CTP:phosphocholine cytidylyltransferase revealed via limited proteolysis and mass spectrometry.

CTP:phosphocholine cytidylyltransferase (CCT) is a multi-domain enzyme that regulates phosphatidylcholine synthesis. It converts to an active form upon binding cell membranes, and interdomain dissociations have been hypothesized to accompany this process. To identify these interdomain and membrane interactions, the tertiary structures of three forms of CCTalpha were probed by monitoring accessibility to proteases. Time-limited digestion with chymotrypsin or arginine C of soluble CCTalpha (CCT(sol)), phospholipid vesicle-bound CCT (CCT(mem)), and a soluble constitutively active CCT truncated at amino acid 236 generated complex mixtures of peptides that were resolved and identified by gel electrophoresis/immunoblotting and by matrix-assisted laser desorption/ionization-mass spectrometry, with or without coupling to capillary liquid chromatography. Identification of cleavage sites enabled assembly of peptide bond accessibility maps for each CCT form. Our results reveal a approximately 80-residue core within the catalytic domain (domain C) as the most inaccessible region in all three forms and the C-terminal phosphorylation domain as the most accessible. Membrane binding has little effect on the protease accessibility of these domains. To map the protease sites onto the catalytic domain, its three-dimensional structure was modeled from the atomic coordinates of glycerol-phosphate cytidylyltransferase (Protein Data Bank code 1COZ). The protease inaccessibility of most sites in domain C could be explained by burial or location within secondary structural elements. The accessibility of the N-terminal domain (domain N) was enhanced upon membrane binding. Residues Phe(234)-Leu(303) were inaccessible in CCT(mem), suggesting burial in the membrane. Surprisingly, residues Leu(274)-Leu(303) of this domain were also inaccessible in CCT(sol). We propose that this region is buried by interdomain contacts with domain N in CCT(sol). Membrane binding and burial of domain M in the lipid bilayer may disrupt this interaction, leading to increased exposure of sites in domain N.

Amino Acid Sequence↗
PubMed2002

Molecular dynamics simulations of a calmodulin-peptide complex in solution.

We have performed an 4-ns MD simulation of calmodulin complexed with a target peptide in explicit water, under realistic conditions of constant temperature and pressure, in the presence of a physiological concentration of counterions and using Ewald summation to avoid truncation of long-range electrostatic forces. During the simulation the system tended to perform small fluctuations around a structure similar to, but somewhat looser than the starting crystal structure. The calmodulin-peptide complex was quite rigid and did not exhibit any large amplitude domain motions such as previously seen in apo- and calcium-bound calmodulin. We analyzed the calmodulin-peptide interactions by calculating buried surface areas, CHARMM interaction energies and continuum model interaction free energies. In the trajectory, the protein surface area buried by contact with the peptide is 1373 A(2) approximately evenly divided between the calmodulin N-terminal, C-terminal and central linker regions. A majority of this buried surface, 803 A(2), comes from nonpolar residues, in contrast to the protein as a whole, for which the surface is made up of mostly polar and charged groups. Our continuum calculations indicate that the largest favorable contribution to peptide binding comes from burial of molecular surface upon complex formation. Electrostatic contributions are favorable but smaller in the trajectory structures, and actually unfavorable for binding in the crystal structure. Since nonpolar groups make up most of buried surface of the protein, our calculations suggest that the hydrophobic effect is the main driving force for binding the helical peptide to calmodulin, consistent with thermodynamic analysis of experimental data. Besides the burial of nonpolar surface area, secondary contributions to peptide binding come from burial of polar surface and electrostatic interactions. In the nonpolar interactions a crucial role is played by the nine methionines of calmodulin. In the electrostatic interactions the negatively charged protein residues and positively charged peptide residues play a dominant role.

Algorithms↗
PubMed2006

Wet-season dormancy release in seed banks of a tropical leguminous shrub is determined by wet heat.

BACKGROUND AND AIMS: Hard-seeded (physical) dormancy is common among plants, yet mechanisms for dormancy release are poorly understood, especially in the tropics. The following questions are asked: (a) whether dormancy release in seed banks of the tropical shrub Parkinsonia aculeata (Caesalpiniaceae) is determined by wet heat (incubation under wet, warm to hot, conditions); and (b) whether its effect is modified by microclimate. METHODS: A seed burial trial was conducted in the wet-dry tropics (northern Australia) to compare dormancy release across different habitats (open, artificial cover, ground cover and canopy cover), burial depths (0, 3 and 20 cm) and burial durations (2, 6 and 14 weeks). Results were compared with predictions using a laboratory-derived relationship between wet heat and dormancy release, and microclimate data collected during the trial. KEY RESULTS: Wet heat (defined as the soil temperature above which seeds were exposed to field capacity or higher for a cumulative total of 24 h) was 43.6 degrees C in the 0 cm open treatment, and decreased with increasing shade and depth to 29.5 degrees C at 20 cm under canopy cover. The dormancy release model showed that wet heat was a good predictor of the proportion of seeds remaining dormant. Furthermore, dormancy release was particularly sensitive to wet heat across the temperature range encountered across treatments. This resulted in a 16-fold difference in dormancy levels between open (<5 % of seeds still dormant) and covered (82 %) microhabitats. CONCLUSIONS: These results demonstrate that wet heat is the principal dormancy release mechanism for P. aculeata when conditions are hot and wet. They also highlight the potential importance of microclimate in driving the population dynamics of such species.

Fabaceae↗
PubMed1999

Autologous latissimus breast reconstruction in association with the abdominal advancement flap: a new refinement in breast reconstruction.

The authors present a technique that combines autologous latissimus breast reconstruction with the thoracoabdominal advancement flap. The aim is to reduce the patched effect of the dorsal skin paddle and to minimize scars on the reconstructed breast. Fifty patients underwent delayed breast reconstruction using this technique from March 1993 through May 1997. Of these 50 patients, 42 (84%) had unilateral reconstruction and 8 (16%) had two-stage bilateral reconstruction at 5- to 7-month intervals. Forty-one patients (82%) had previously received radiotherapy of the thoracic wall. The abdominal advancement flap allowed subtotal burial of the latissimus dorsi flap (preserving only the future nipple-areolar complex) in 40 patients (80%) and total burial in 10 patients (20%). Reduction surgery was done on the other breast in 17 patients (34%) and mastopexy in 3 patients (6%). In 8 patients (16%) the opposite breast required mastectomy and reconstruction using an autologous latissimus dorsi flap. The aesthetic results, as evaluated by two plastic surgeons on the basis of pre- and postoperative photographs, were rated as very good in 44 patients (88%), good in 5 patients (10%), and poor in 1 patient (2%). No result was considered bad. The main drawback was dorsal seroma, which occurred in 68% of patients but was managed easily by repeated aspiration. Subtotal or total burial of the skin paddle through the original association of the autologous latissimus dorsi flap with the abdominal advancement flap gives markedly improved results by reducing the scars on the reconstructed breast, avoiding the patched effect, and providing a supple breast with a natural ptotic shape.

Abdomen↗
PubMed1995

Biodegradation of radioactive animals.

The two most common disposal alternatives for animals contaminated with radioactive materials are incineration and burial. For most of the country burial has entailed shipping the carcasses to a commercial disposal facility at Barnwell, South Carolina, where it was landfilled along with other solid radioactive waste. Unfortunately, since 30 June 1994, this facility accepts waste generated by the states of the Southeast Compact only. Therefore, burial is no longer an option for most of the country's generators and incineration is an option only for those institutions which have, or have access to, an incinerator that is permitted to burn radioactive materials and that accepts animal carcasses with de minimis levels of radioactive contaminants. Many institutions, especially those in congested urban areas where the public does not support incineration, do not have viable outlets for radioactive animal carcasses. Interim, on-site storage poses problems of its own. Biodegradation of animal carcasses with dermestid beetles is an inexpensive approach to this waste management problem.

Animals↗
PubMed2000

Implementation of the MARSSIM philosophy to evaluate the remedial status of a radioactive waste disposal site at the Idaho National Engineering and Environmental Laboratory. Multi-Agency Radiation Survey and Site Investigation Manual.

Implementation of the MARSSIM remedial-verification protocol at a radioactive waste disposal site is described in some detail to provide a record of the utility of this process. The selected site was the Stationary Low-Power Reactor No. 1 burial ground at the Idaho National Engineering and Environmental Laboratory. Evaluation was restricted to 137Cs in the uppermost 10 cm of potentially contaminated soils. According to the MARSSIM, this site warranted a "Class 1" designation based on previous remedial activities within the burial ground, its status as a radioactive disposal facility, and the anticipated presence of discrete radioactive particles. Nine survey units within the confines of the burial ground were selected, based primarily on the presence of physical boundaries and disparate histories. Surface scans with 100% coverage were performed using a hand-held plastic scintillator and rate meter with audible output. In situ gamma-ray spectrometry was not used for the individual stationary measurements due to the limited area and proximity of engineered barriers. Instead, individual soil samples were obtained using a standard hand-held coring device. The number of soil samples taken from the background reference area and each survey unit were determined with the MARSSIM protocol, which resulted in a total of 160 (including quality-control samples). Two of the nine regions exhibited elevated radiation levels and the null hypothesis could not be rejected in one survey unit, thereby indicating the need for additional remediation. The MARSSIM process proved to be flexible, scientifically rigorous, and cost effective in this field application. Several modifications to the procedure are discussed and offered as recommendations for enhancement of the MARSSIM.

Humans↗
PubMed1996

Seasonal variations in the isolation of Salmonella typhimurium, Salmonella enteritidis, Bacillus cereus and Clostridium perfringens from environmental samples.

Calf carcasses contaminated with S. typhimurium, B. cereus and Cl. Perfringens were placed in either a decomposition pit or in a deep burial pit. Salmonella was isolated from the soil around the decomposition pit for 27 weeks and for 15 weeks around the burial site. Salmonella re-appeared in soil samples during cold winter weather after an apparent 9-week absence from the decomposition pit and after 68 weeks in the burial site (a total of 88 weeks after the start of the experiment). There was also an annual rise in the isolation rate of B. cereus from the soil during the colder winter months, but Cl. perfringens appeared to be more prevalent in samples taken during spring of the second year of the study. A similar apparent rise in the prevalence of S. enteritidis during a cold winter period occurred in an empty poultry house that had previously held a naturally infected broiler-breeder flock.

Animals↗
PubMed1987

A study of the haptic bearing angles in eyes with the Optiflex anterior chamber implant.

Gonioscopy and goniophotography were performed on 137 eyes with the Optiflex angle supported implant. At the time of gonioscopy the lenses had been in situ for a median of 20 months, with a range of 3-38 months. In 75.9% of cases one or both haptics were positioned posterior to the scleral spur with some degree of iris push. Iris tuck was seen in 29.2% of cases. Three different types of fibrous tissue formations were seen in the angles. The first two types (sleeving and iris haptic adhesions) occurred in the majority of cases and were haptic related. The third type was in the form of true peripheral anterior synechiae and occurred in 17.5% of cases. In cases with haptic related adhesions only, the angle remained open. Secondary glaucoma developed in 12 cases (8.7%). Ten cases had open angles. In the remaining two cases peripheral anterior synechiae were present in more than two-thirds of the angle, which was considered to be closed. Total burial of one of the haptics occurred in 25.5% of cases. A prominent iris vessel was observed near one of the haptics in nine cases. The thin looped haptics appear to stimulate fibrous tissue formation in the majority of cases. The haptic related adhesions add to the stability of the implant. It would make dislocation of the lens unlikely, even under severe trauma to the eye. However, once formed it would make removing the implant virtually impossible without severing the haptics. With time and with burial, the haptics seem to move away from the direction of the cornea. Total insulation of the haptic from the peripheral cornea is achieved with the occurrence of total burial.

Eye↗
PubMed2004

Surgical treatment of superficial peroneal neuroma.

BACKGROUND: Several techniques have been described for the surgical treatment of symptomatic superficial peroneal neuromas, including transection of the nerve with burial in muscle or bone to prevent recurrence. METHODS: We compared in 27 consecutive patients the results of transection and burial of the proximal peroneal nerve stump into muscle (group A) with results of transection and burial of the proximal stump into bone (group B). RESULTS: The perceived pain relief and improvement in mean pain score were significantly higher (p < .05) in group B than in group A. In addition, four patients in group A required revision neurotomy compared to none in group B. CONCLUSION: For symptomatic superficial peroneal neuromas, transection with transposition of the proximal nerve stump into bone provides superior results compared with those of neurotomy with transposition of the proximal stump into muscle.

Adult↗
PubMed1993

Mozart's chronic subdural hematoma.

No commemoration of the bicentennial of Mozart's death would be complete without some consideration of that premature yet predictable demise. Mozart's premonitions of death are well known and apparently played a role in the composition of the K.626 Requiem and perhaps other works. His death has traditionally been ascribed to infectious causes, chiefly rheumatic fever or post-streptococcal glomerulonephritis, exacerbated by intemperance and chronic penury. Pathology has been difficult because of his supposed burial in a pauper's grave, the location and contents of which were later supposedly lost. Mozart's burial place in St. Mark's Cemetery in Vienna was known and, in the parlance of the day, "reorganized" a decade later, as the occupants of plots were disinterred to make room for the more recently decreased. A skull believed to the Mozart's was saved by the successor of the gravedigger who had supervised Mozart's burial, and then passed into the collections of the anatomist Josef Hyrtl, the municipality of Salzburg, and the Mozarteum museum (Salzburg). Forensic reconstruction of soft tissues related to this skull reveals substantial concordance with Mozart's portraits. The skull suggests premature closure of the metopic suture, which has been suggested on the basis of his physiognomy. A left temporal fracture and concomitant erosions raise the question of chronic subdural hematoma, which would be consistent with several falls in 1789 and 1790 and could have caused the weakness, headaches, and fainting he experienced in 1790 and 1791. Aggressive bloodletting to treat suspected rheumatic fever could have decompensated such a lesion to produce his death on December 5, 1791.

Austria↗
PubMed1985

Waste disposal technologies for polychlorinated biphenyls.

Improper practices in the disposal of polychlorinated biphenyl (PCB) wastes by land burial, chemical means and incineration distribute these chemicals and related compounds such as polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzodioxins (PCDDs) throughout the environment. The complete range of methods for disposal that have been proposed and are in use are examined and analyzed, with emphasis given to the two most commonly used methods: land burial and incineration. The understanding of aquifer contamination caused by migration of PCBs from subsurface burial sites requires a description of the physical, chemical and biological processes governing transport in unsaturated and saturated soils. For this purpose, a model is developed and solved for different soil conditions and external driving functions. The model couples together the fundamental transport phenomena for heat, mass, and moisture flow within the soil. To rehabilitate a contaminated aquifer, contaminated groundwaters are withdrawn through drainage wells, PCBs are extracted with solvents or activated carbon and treated by chemical, photochemical or thermal methods. The chemical and photochemical methods are reviewed, but primary emphasis is devoted to the use of incineration as the preferred method of disposal. After discussing the formation of PCDFs and PCDDs during combustion from chloroaromatic, chloroaliphatic, as well as organic and inorganic chloride precursors, performance characteristics of different thermal destructors are presented and analyzed. To understand how this information can be used, basic design equations are developed from governing heat and mass balances that can be applied to the construction of incinerators capable of more than 99.99% destruction with minimal to nondetectable levels of PCDFs and PCDDs.

Benzofurans↗
PubMedDate not supplied

Carbonate petrography, kerogen distribution, and carbon and oxygen isotope variations in an early Proterozoic transition from limestone to iron-formation deposition, Transvaal Supergroup, South Africa.

The transition zone comprises Campbellrand microbialaminated (replacing "cryptalgalaminate") limestone and shale, with minor dolomite, conformably overlain by the Kuruman Iron Formation of which the basal part is characterized by siderite-rich microbanded iron-formation with minor magnetite and some hematite-containing units. The iron-formation contains subordinate intraclastic and microbialaminated siderite mesobands and was deposited in deeper water than the limestones. The sequence is virtually unaltered with diagenetic mineral assemblages reflecting a temperature interval of about 110 degrees to 170 degrees C and pressures of 2 kbars. Carbonate minerals in the different rock types are represented by primary micritic precipitates (now recrystallized to microsparite), early precompactional sparry cements and concretions, deep burial limpid euhedral sparites, and spar cements precipitated from metamorphic fluids in close contact with diabase sills. Paragenetic pathways of the carbonate minerals are broadly similar in all lithofacies with kerogen intimately associated with them. Kerogen occurs as pigmentation in carbonate crystals, as reworked organic detritus in clastic-textured carbonate units, and as segregations of kerogen pigment around late diagenetic carbonate crystals. Locally kerogen may also be replaced by carbonate spar. Carbon isotope compositions of the carbonate minerals and kerogen are dependent on their mode of occurrence and on the composition of the dominant carbonate species in a specific lithofacies. Integration of sedimentary, petrographic, geochemical, and isotopic results makes it possible to distinguish between depositional, early diagenetic, deep burial, and metamorphic effects on the isotopic compositions of the carbonate minerals and the kerogen in the sequence. Major conclusions are that deep burial thermal decarboxylation led to 13C depletion in euhedral ferroan sparites and 13C enrichment in kerogen (organic carbon). Metamorphic sparites are most depleted in 13C. Carbonates in oxide-rich iron-formations are more depleted in 13C than those in siderite-rich iron-formation whereas the kerogens in oxide banded iron-formations (BIF) are more enriched. This implies that the siderite-rich iron-formations were not derived from oxide-rich iron-formation through reduction of ferric iron by organic matter. Organic matter oxidation by ferric iron did, however, decrease the abundance of kerogen in oxide-rich iron-formation and led to the formation of isotopically very light sparry carbonates. Siderite and calcmicrosparite both represent recrystallized primary micritic precipitates but differ in their 13C composition, with the siderites depleted in 13C by 4.6 per mil on average relative to calcmicrosparite. This means that the siderites were precipitated from water with dissolved inorganic carbon depleted in 13C by about 9 per mil relative to that from which the limestones precipitated. This implies an ocean system stratified with regard to total carbonate, with the deeper water, from which siderite-rich iron-formation formed, depleted in 13C. Iron-formations were deposited in areas of very low organic matter supply. Depletion of 13C may, therefore, derive not from degradation of organic matter but from hydrothermal activity, a conclusion which is supported by 18O composition of the carbonate minerals and trace element and rare earth element (REE) compositions of the iron-formations.

Calcium Carbonate↗